Transcript ZOO 366-Comparative Vertebrate Anatomy

ZOO 366-Comparative Vertebrate
Anatomy
By
Dr. O.A Oke
Department of Biological Sciences
University of Agriculture, Abeokuta,
Nigeria.
THE ALIMENTARY SYSTEM
INTRODUCTION
invaginated to form a stomodeum and
proctodeum respectively. The wall of
the alimentary canal is completed by
tissue of mesodermal (splanchnic)
origin and consisits mainly of muscle
and connective tissue together with the
blood vessels and nerves. Outwardly
the tube is invested by the peritoneum (
coelomic epithelium), which also
covers the mesenteries by which it is
suspended in the body.
in the embryo as a simple straight tube,
but in the adult it is differentiated into
regions which differ according to the
particular work carried out therein. The
tube is usually much longer than the
body, so that since the two ends fixed,
it is thrown into coils.
The main regions of the alimentary
canal are the buccal cavity, pharynx,
esophagus, stomach and intestine.
variable shaped, movable, muscular
tongue is found on the floor of the
buccal cavity. In many instances, even
in the lower vertebrates, there is no
clear line of demarcation between the
buccal cavity and the next region, the
pharynx, but developmentally the
former is lined with ectoderm and the
latter by endoderm. The two regions
can be called the bucco-pharyngeal
region.
found in air-breathing vertebrates,
originate. The lungs may arise directly
from a layngcal chamber or when a
neck is present, as in the mammals,
they are situated at the end of a tubular
trachea. In those vertebrates where the
majority of the visceral clefts have
been lost, the pharyngeal part of the
first cleft is retained as part of the
auditory apparatus to form Eustachian
tube and tympanic chamber.
the flattening of the tube or the folding
of its lining, the lumen is considerably
reduced. The oesophagus forms a
connecting channel between the
pharynx and the next region, the
stomach.
escape of the food from the stomack
into the intestine is guarded against by
the development in the wall of the
distal (pyloric) end of the stomach of a
ring of muscle termed a sphincter, the
pyloric sphincter, which closes the
aperture and only opens under certain
conditions. The position of this
sphincter is usually marked externally
by a constriction, the pyloric
constriction. In the wall of the stomach
intestine is the region where a great
part of digestion and most of the
aborption of the digested food takes
place. And is appropriately modified in
different vertebrates. The lining
epithelium provides numerous glands,
the products of which are poured out
on to the food. The form of this region
varies considerably in different
vertebrates as also does its
terminology, any details must be left to
the description of individual examples.
muscular contraction of a rhymical
character which pass along the length
of the tube, pushing the food in front of
the constricted region. This rhythmical
contraction is termed peristalsis.
these regions. The liver and pancreas,
already mentioned as opening by their
ducts into the duodenum, arise in
some animals 9e.g chick0 as
outgrowths of the endoderm of the
alimentary canal, but soon mesodermal
derivatives become incorporated with
these outgrowths to form the adult
glands, the connection between the
gland and the intestine being retained
as the duct. The secretions of these
glands, bile and pancreatic juice, play
In addition to these special glands, the
lining epithelium of all regions of the
alimentary canal contains numerous
mucous glands.
VILL. THE URINARY ORGANS
capillaries. The adrenal gland lies on
its ventral surface. The kindney is
bathed in the lymph which is contained
in the cisteria magna and its drained
into the veins of the kidney. These are
the renal veins and the renal portal
vein. Renal arteries supply the kidney.
Bowman’s capsule into which pushes
an affercent arteriole that branches off
then leaves away the corpuscle as an
efferent arteriole. The tuft of vessels
thus formed insiude the corpuscle is
called the glomerulus. (The efferent
arteriole breaks up, outside the
glomerulus, into capillaries which
connect with those of the renal portal
vein).
convoluted and ultimately opens into a
collecting tubule. The collecting
tubules pour the urine into the Wolffian
duct which extends along the outer
lateral border of the kidney.
Search for the above mentioned
structure in the section. These are:
thelateral edge of the organ, lined by a
simple cubical epithelium and
surrounded by connective tissue and
unstriated muscle fibres.
the Wolffian duct. It may contain
blood corpuscles and its wall consists
of the usual layers characteristic of
veins.
- The renal artery an renal are
conspicuous on the ventral side of the
kidney
-
The adrenal gland lies on the
ventral surface, and consists of
glandular cells which are surrounded
by numerous blood vessels.
the nephrostomes or peritoneal funnels
are found on the ventral side of the
section. Each peritoneal funnel is lined
largely with ciliated cuboidal cells.
corpuscles are found each of the
glomerulus in the middle, and of the
Bowman’s capsule to the outside. The
wall of the latter is built up of a simple
squanmous epithelium.
tubules are lined by large granular cells
and each have a narrow lumen. They
are the greatest elements of the kidney
in number.
the section lined by cuboidal cells
which contain but few granules and
have a wide lumen. They are mush
fewer in number that the uriniferous
tubules.
- A network of blood vessels and
capillaries is held by connective tissue
among the tubules.
THE GENITAL GLANDS (GONADS)
sex, thus the testis in the male
produces the spermatozoa, while the
ovary in the female product the ova
(sing.ovum).
THE TESTIS
these tubules in the mature testis. The
tubules are held together by an
intertubular connective tissue which
contains particular interstitial cells that
secrete certain hormones which are
responsible for the appearance of the
secondary sexual characters.
a series of phase till it reaches its final
form, the wall of the seminferous
tubule thus contains all that represent
these phases. The process is known as
spermatogenesis.
Examine and note:
rounded or oval in section, each
surround by a thin basement
membrane and contains in its wall
several layers of cells representing
(from outside inwards)
(i) The spermatogonia lie along
the periphery of the tubule and
appear closely packed together..
(ii) The primary spermatocytes are
the largest of the cells and have
large nuclei.
(iii) The secondary spermatocytes
are smaller than the preceding cells,
about half size, and their nuclei
stain deeply.
(iv) The spermatids are still smaller
than the preceding cells and their
nuclei are more condense. They
aggregate in clusters.
grouped in clusters and some
appear connected with peculiar
large cells which lie at the
periphery of the tubule. These are
cells of Sertoli.
A spermatozoon (or sperm) has an
elongated head and a long delicate
tail. Its nucleus lies in the head
which is pointed at the acrosome.
stages in the seminiferous tubule
with the help of the H.P. and
proceed studying other structures of
the testis:
of connective tissue which holds
the tubules together and contains
blood vessels. It also contains cells
of endocrine secretion, the
interstitial cells.
fibrous connective tissue and
surrounds the testis. The
intertubular tissue extends to the
periphery of the testis where it is
connected with this sheath.
-The peritoneal epithelium is the
outermost covering of the testis.
3
THE OVARY
However, the ova (eggs) are very
much larger in size than the sperms,
since the ova represent the nonmotile and food storing gametes.
The sperms, on the other hand,
ought to be very small because they
are motile. They are also formed in
much greater numbers than the ova.
104
I.T.S of the ovary of the toad
of hallow lobules in which the ova
are formed. Each lobule is
surrounded externally by the theca
externa, which corresponds to the
peritoneal epithelium of the testis.
envelope which contains unstriated
muscle fibres, blood vessels and
nerves. The theca interna,
however,is incomplete where the
sac is connected to the outer wall of
the ovary. It is this place at which
the ovum, when fully mature,
bursts out to fall into the body
cavity.
The ovum is also surrounded by a
number of cells form the ovarian
stroma which is responsible for the
secretion of the ovarian hormones.
The ovum passes through a number
of phases following the oogonium
stage. First is the primary oocyte
which increases in size gradually.
Its nucleus also undergoes certain
changes and shows several
nucleoli.
Finally a vitelline membrance is
formed around the primary oocyte,
which separates it from the
follicular cells.
oviduct, thus becoming the
secondary oocyte. The second
maturation division occurs on
fertilization, that is, externally in
water.87
The Mammalian Circulation
aorta, the main artery of the body.
From this numerous arteries, some
median and paired, convey blood to
the capillary systems in the organs
and tissues, where gaseous
exchange takes place.
Corresponding veins convey the
deoxygenated blood to the venae
cavae (great veins) by which it is
returned to the right atrium. The
walls of the arteries and veins are
responsible for pumping the blood,
the heart is of the utmost
importance in maintaining the
tissues in a state of health and
efficiency. The capillaries represent
the place where exchange of
materials takes place, and as such
provide the raison d’etre
for the circulatory system. We shall
deal with these two parts of the
circulatory in turn.